This application claims priority under 35 USC 119 of Japanese Patent Application No. 2001-61032 filed in JPO on Mar. 6, 2001, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a cleaner-less type image forming apparatus and method (hereafter called a cleaner-less image forming apparatus) that can prevent cleaning efficiency from reducing and maintain high print quality.
2. Description of the Related Art
A transfer roller, a charge brush, and a memory removal brush are made to contact with a photoconductive body in the cleaner-less image forming apparatus adopting a contact transferring method. A sheet of paper is carried with the sheet sandwiched in between the transfer roller and the photoconductive body, and at this time, a toner image formed on the photoconductive body is transferred to the sheet by applying a predetermined bias to the transfer roller.
The charge brush and the memory removal brush are obviously more contaminated or stained as the number of sheets of paper which have been printed grows. For this reason, a transfer bias is preliminarily applied to the transfer roller within an interval which is a period from the time one sheet of paper passes the transfer roller to the time the next sheet reaches the transfer roller, before printing is carried out, in order to clean these brushes.
As the brushes are more contaminated, however, the preliminary bias voltage that is applied in a usual case cannot fully eliminate the contamination of the brushes. When using a brush charger, it is difficult to keep charge potential on a surface of the photoconductive body uniform, especially due to the toner adhered to the brush, etc. This is because the toner is made up from particles which are insulators, and an electric current between the charge brush and the surface of the photoconductive body is reduced due to the particles adhered to fibers of the charge brush.
Further, the memory removal brush cannot fully disperse the residual toner remaining on the surface of the photoconductive body as a large quantity of toner is adhered to the removal brush, and there is a problem of reducing cleaning efficiency. That is why the image of the previous page appears on the next page, i.e., a so-called memory occurs, and the residual toner on the surface of the photoconductive body is adhered to the sheet of paper, i.e., so-called fog is generated, so that there is a problem of reducing print quality. Additionally, a problem of toner on the backside of a sheet happens such that the residual toner on the surface of the photoconductive body is adhered to the transfer roller, and the toner of the transfer roller is further adhered to the backside of the sheet.
The present invention is provided in view of the above problems, and it is an object of the present invention to provide a cleaner-less image forming apparatus and method that can prevent cleaning efficiency from reducing and maintain high print quality.
In order to accomplish the aforementioned object, the image forming apparatus of the present invention includes a photoconductive body, a charge member for charging a surface of the photoconductive body, a transfer member which is disposed so as to contact with the photoconductive body and transfers a toner image on the photoconductive body to a sheet of paper, a memory removal member for dispersing residual toner remaining on the photoconductive body, and a controller for changing a preliminary bias in accordance with a print workload that the apparatus has had and applying the preliminary bias to the transfer member before applying a transfer bias to the transfer member.
With the apparatus, it is possible to prevent contamination of the photoconductive body, the transfer member, the charge member, and the memory removal member because the preliminary transfer bias is applied to the transfer member (the pre-transfer bias is applied) before applying the transfer bias to the transfer member, that is to say, before printing is carried out. Therefore, the toner can be removed from the charge member, so that the surface of the photoconductive body can be uniformly charged. Moreover, the toner can be removed also from the memory removal member, so that cleaning efficiency can be prevented from reducing. Furthermore, it is possible to prevent the toner from adhering to a surface of the transfer member, and to prevent the toner from adhering to a backside of a sheet.
According to one aspect of the present invention which is one of the greatest characteristics of the present invention, the pre-transfer bias voltage is changed in accordance with the print workload, so that the above-described effects are more improved and maintained. In other words, as the print workload increases more (for example, the accumulated number of sheets of paper which have been printed increases, or an accumulated period of time for which the photoconductive body has been being worked increases), the pre-transfer bias voltage is made to be higher, and the high cleaning efficiency is maintained. Additionally, the pre-transfer bias may be being applied to the transfer member for a period which the photoconductive body takes to rotate once or more.
Meanwhile, the pre-transfer bias is preferably changed in accordance with not only the print workload but also a surrounding condition such as a temperature or humidity because resistance of the transfer member varies in accordance with the surrounding condition. In this manner, it is possible to obtain a still more optimum pre-transfer bias voltage when printing is to be carried out.
Additional objects, aspects, benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention pertains from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings.